The present invention relates to a method and apparatus for indirectly measuring the thermal energy supplied to a number of user stations such as apartments, zones, etc.
Two kinds of measurement of the supplied heat are generally known: the direct method and the indirect one. The direct method involves the direct measurement of all the variables that are required to determine the amount of heat utilized, such as the mass of heating fluid flow, and the differential temperature .DELTA.t between the delivery and the return pipes from which the exact amount of heat transferred to the consumer can be calculated. Conversely, according to the indirect method, only some variables are directly measured, and the values of the other variables are introduced as constants or functions of measured values.
The simplest and most used indirect method is the one consisting of measuring only the service utilizing time, and it is usually carried out by using an electrical hour-counter, electrically connected in parallel with a zone valve, which can interrupt or allow the flow of the heat carrier medium upon user demand. In this way, the measurement of a single variable (demand time) allows the amount of the heat utilized by each user's station to be indirectly measured and therefore allows costs of the heat production to be shared proportionally to the time of use.
Due to the energy crisis and the costs of heat production consequently exponentially increasing, the methods for counting the heat consumption have had to be refined in order to make the users more responsible. In fact, by using the method based on the single hour-counter, the user who consumes heat at a lower temperature was penalized, whereas the user who consumes heat at a higher temperature was injustly favoured. Furthermore, the hour-counter operates, i.e. counts, without taking into consideration the differences between heat transfer ratings, i.e. number, size or efficiency of elements or registers, in each apartment or zone.